Fix: Get the type of Chain.create() from its application (#407)

* Get the type of Chain.create() from its application

* Add test contract

* Update CHANGELOG.md

* Update the tests

* Update tests again

CHANGELOG.md

@@ -8,6 +8,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 ### Changed
 ### Removed
+### Fixed
+- [404](https://github.com/aeternity/aesophia/issues/404) Contract polymorphism crashes on non-obvious child contract typing.
 
 ## [7.0.0]
 ### Added

src/aeso_ast_to_fcode.erl

@@ -693,7 +693,7 @@ expr_to_fcode(Env, _Type, {app, _Ann, {Op, _}, [A]}) when is_atom(Op) ->
     end;
 
 %% Function calls
-expr_to_fcode(Env, Type, {app, _, Fun = {typed, _, FunE, {fun_t, _, NamedArgsT, ArgsT, _}}, Args}) ->
+expr_to_fcode(Env, _, {app, _, Fun = {typed, _, FunE, {fun_t, _, NamedArgsT, ArgsT, Type}}, Args}) ->
     Args1 = get_named_args(NamedArgsT, Args),
     FArgs = [expr_to_fcode(Env, Arg) || Arg <- Args1],
     case expr_to_fcode(Env, Fun) of

test/aeso_compiler_tests.erl

@@ -202,6 +202,7 @@ compilable_contracts() ->
      "polymorphism_contract_interface_extensions",
      "polymorphism_contract_interface_same_decl_multi_interface",
      "polymorphism_contract_interface_same_name_same_type",
+     "polymorphism_variance_switching_chain_create",
      "missing_init_fun_state_unit",
      "complex_compare_leq",
      "complex_compare",
@@ -1025,6 +1026,20 @@ failing_contracts() ->
                      "Cannot unify `Animal` and `Cat` in a covariant context\n"
                      "when checking the type of the pattern `q15 : oracle_query(Cat, Cat)` against the expected type `oracle_query(Cat, Animal)`">>
                   ])
+    , ?TYPE_ERROR(polymorphism_variance_switching_chain_create_fail,
+                  [<<?Pos(9,22)
+                     "I is not implemented.\n"
+                     "when resolving arguments of variadic function `Chain.create`">>,
+                   <<?Pos(10,13)
+                     "Cannot unify `I` and `C` in a covariant context\n"
+                     "when checking the type of the pattern `c2 : C` against the expected type `I`">>,
+                   <<?Pos(10,22)
+                     "I is not implemented.\n"
+                     "when resolving arguments of variadic function `Chain.create`">>,
+                   <<?Pos(11,22)
+                     "I is not implemented.\n"
+                     "when resolving arguments of variadic function `Chain.create`">>
+                  ])
     , ?TYPE_ERROR(missing_definition,
                   [<<?Pos(2,14)
                      "Missing definition of function `foo`">>

test/contracts/polymorphism_variance_switching_chain_create.aes

@@ -0,0 +1,29 @@
+contract interface I =
+    entrypoint f : () => int
+
+contract C1 : I =
+    entrypoint f() = 123
+
+contract C2 : I =
+    entrypoint f() = 888
+
+namespace Make =
+    stateful function new1() : I = Chain.create() : C1
+    stateful function new2() : I = Chain.create() : C2
+
+    stateful function new(c : I) : int = c.f()
+
+main contract Main =
+    stateful entrypoint test1() =
+        let c = Make.new1()
+        Make.new(c)
+
+    stateful entrypoint test2() =
+        let c = Make.new2()
+        Make.new(c)
+
+    stateful entrypoint test3() =
+        let c1      = Chain.create() : C1  // succeeds
+        let c2 : I  = Chain.create() : C1  // succeeds
+        let c3 : C1 = Chain.create()       // succeeds
+        ()

test/contracts/polymorphism_variance_switching_chain_create_fail.aes

@@ -0,0 +1,12 @@
+contract interface I =
+    entrypoint f : () => int
+
+contract C : I =
+    entrypoint f() = 123
+
+main contract Main =
+    stateful entrypoint test() =
+        let c1 : I = Chain.create()       // fails
+        let c2 : C = Chain.create() : I   // fails
+        let c3     = Chain.create() : I   // fails
+        ()